1. Field of the Invention
The present invention relates to polyimides which are obtainable by reacting
A) a dianhydride component consisting of
a.sub.1) from 50 to 100 mol % of at least one dianhydride of the formula I ##STR1## where R is a tetravalent aromatic or heteroaromatic radical, with the exception of ##STR2## and a.sub.2) from 0 to 50 mol % of a pyromellitic dianhydride with PA1 b.sub.1) from 50 to 100 mol % of at least one diamine of the formula II ##STR3## where R.sup.1 to R.sup.4, independently of one another, are identical or different and are hydrogen, halogen, C.sub.1 -C.sub.12 -alkyl, C.sub.1 -C.sub.12 -alkoxy, C.sub.5 --C.sub.7 -cycloalkyl, C.sub.6 -C.sub.18 -aryl, C.sub.4 - or C.sub.5 -hetaryl or C.sub.1 -C.sub.12 -alkyl-C.sub.6 -C.sub.18 -aryl, PA1 R.sup.5 and R.sup.6, independently of one another, are identical or different and can be individually selected for each C atom in the alicyclic ring and are hydrogen, C.sub.1 -C.sub.12 -alkyl, C.sub.1 -C.sub.12 -alkoxy, C.sub.5 -C.sub.7 -cycloalkyl, C.sub.6 -C.sub.18 -aryl, C.sub.4 - or C.sub.5 -hetaryl or C.sub.1 -C.sub.12 -alkyl-C.sub.6 -C.sub.18 -aryl, and PA1 m is an integer from 4 to 7, and PA1 b.sub.2) from 0 to 50 mol % of at least one diamine of the formula III ##STR4## where X, Y and Z, independently of one another, are identical or different and are a chemical bond or are selected from the group consisting of --O--, --CO--, --S--, --SO.sub.2 --, --C(CH.sub.3).sub.2 --, --C(CF.sub.3).sub.2 -- and --Si(CH.sub.3).sub.2 -- and PA1 r and s, independently of one another, are identical or different and are 0 or 1,
B) a diamine component consisting of
with the proviso that the component A is a mixture of a.sub.1 and a.sub.2 if the component B consists only of b.sub.1 and component B is a mixture of b.sub.1 and b2 if the component A consists only of a.sub.1. The present invention furthermore relates to the use of these polyimides. 2. Description of the Art
Polyimides based on dianhydrides a.sub.1 and a.sub.2 and diamines b.sub.1 were disclosed in EP-A1-398 092. Such polyimides are used for the preparation of liquid crystal displays since they promote the orientation of the liquid crystals. Specific diamines having cycloaliphatic rings for the preparation of polyimides for the same intended use are described in EP-A 368 604 and 439 362. Further diamines of the general formula II for the preparation of plastics or plastics blends are described in EP-A2-379 006.
It is an object of the present invention to provide novel polyimides which are based on the diamines of the general formula II and can be processed by a thermoplastic method but have a higher melt stability and exhibit better heat distortion resistance than the known polyimides.
We have found that this object is achieved by the polyimides defined at the outset. The novel polyimides are obtainable by reacting a dianhydride component A with a diamine component B.
According to the invention, the dianhydride component A is composed of from 50 to 100 mol % of at least one dianhydride al and from 0 to 50 mol % of pyromellitic dianhydride (a.sub.2). The preferably used dianhydride component A consists of from 50 to 99 mol % of a.sub.1 and from 1 to 50 mol % of a.sub.2. A particularly preferably used dianhydride component A consists of from 65 to 99, in particular from 65 to 97, mol % of a.sub.1 and accordingly from 1 to 35, in particular from 3 to 35, mol % of pyromellitic dianhydride. Mixtures of from 70 to 95 mol % of al and from 5 to 30 mol % of a.sub.2 are very particularly preferably used as dianhydride component A.